Boarding houses would work for a single person with no possessions. If you have a partner and/or kids, you need a different solution.
> Mandate that housing needs to have individual bathrooms and kitchens for each unit, mandate that each unit needs a parking space or two, mandate a thousand other useless minutiae under the guise of safety or accessibility that don't actually matter
Many of these mandates exist because retrofitting is impossible. Got three new tenants with cars? Get the backhoe; it's time to build the underground car park. Can't get to the crapper because the doors and bathroom are too small for your wheelchair, and you won't take a dump in diapers? No apartment for you! Low income, have kids and need 3 bedrooms? No room in the boarding house. Go somewhere else.
Universal design is not expensive and makes living spaces more inclusive.